Preparation and Phase Transition Study of a Multi-Environmentally Sensitive Hydrogel

Hydrogels have attracted considerable attention due to their ability to undergo rapid and reversible phase transitions in response to external stimuli. In this work, a novel multi-responsive hydrogel (PT-Gel) was synthesized via the crosslinking of a linear poly(PEGDGE-co-PPGDGE) prepolymer (designated polyPEMPP, where PEMPP stands for Poly(Ethylene glycol) diglycidyl ether-co-Poly(Propylene glycol) diglycidyl ether) with trimethylolpropane tris(2-methyl-1-aziridinepropionate) (T-403), a trifunctional amine crosslinker. The phase transition behavior was evaluated by UV-Vis transmittance measurements at 600 nm as a function of temperature. The phase transition temperature (T_T) of PT-Gels can be precisely tuned from 11.8 ± 0.5 °C to 76.3 ± 1.2 °C by adjusting the hydrophilic poly(ethylene glycol) diglycidyl ether (PEGDGE) content (0-35%), pH (5.0-10.5), NaCl concentration (0-0.9 wt%), and urea concentration (0-0.7 wt%). Specifically, T_T exhibits a nearly linear positive correlation with PEGDGE content and a linear negative correlation with pH, decreasing by 4.8 ± 0.6 °C per pH unit. The addition of 0.9 wt% NaCl lowers T_T by 11.7 ± 0.8 °C through charge screening, while 0.7 wt% urea elevates T_T by 36.5 ± 1.5 °C through hydrogen bond disruption. For the optimal formulation (15% PEGDGE, pH 7.7), T_T and transition width (ΔT) are 34.2 ± 0.6 °C and 4.2 ± 0.3 °C, respectively. PT-Gels demonstrate excellent reversible phase transition behavior, maintaining stable transmittance cycles between 98.7 ± 0.5% and 1.2 ± 0.3% over five consecutive heating-cooling cycles without significant degradation. The main driving forces for the phase transition are identified as hydrophobic interactions, electrostatic repulsion, and hydrogen bonding. This proof-of-concept study provides a rational design strategy for multi-responsive hydrogels with tunable phase transition for applications in smart drug delivery, sensors, and separation systems, while the current limitations include the need for further structural characterization and mechanical property evaluation for specific biomedical applications.